1. Field of the Invention
The present invention relates to the technical field of plastic molding, particularly to a technique for forming a ridge of a resin in a desired form on a polycarbonate substrate.
2. Description of the Related Art
Hereinafter, a conventional technique for forming a ridgy resin film will be described taking an optical recording medium for example.
Reference numeral 110 in FIG. 9 denotes an optical recording medium. The optical recording medium 110 includes a disk-shape substrate 111 made of a transparent resin. A circular hole 113 is provided at the center of the substrate 111.
A recording layer (a reflection film) composed of a metal thin film (a reflection film) and a protective layer for protecting the recording layer are formed on the surface of the substrate 111.
On the back surface of the substrate 111, a resin film 120 constituted of a ridge is formed around the hole 113. The ridgy resin film 120 takes on, as a whole, a ring form, and its center coincides with those of the hole 113 and the substrate 111.
The ridgy resin film 120 and the substrate 111 are formed by injection molding in which a resin is injected into a cavity of a metal mold and then molded. That is, the ridgy resin film 120 and the substrate 111 are molded into a unitary body.
The above-mentioned recording layer is laid outside the ridge of the optical recording medium 110, and the area extending outwardly of the ridge is defined as an information recording area 118. In the information recording area 118, information can be recorded by forming pits or grooves in other than the area where the ridgy resin film 120 has been formed.
A reader which reads out information from the optical recording medium 110 is equipped with a laser beam irradiator, and the optical recording medium 110 is placed on a tray with its ridgy resin film 120 facing downward and inserted into the device such that the recording medium goes above the laser beam irradiator.
With the optical recording medium in this position, the ridgy resin film 120-provided side of the optical recording medium 110 is irradiated with a laser beam. The irradiated laser beam is reflected by the metal thin film and detected to read information recorded thereon.
Since the optical recording medium 110 is placed in such a manner, the ridgy resin film 120 prevents the information recording area 118 from being brought into contact with the tray and consequently being scratched. Moreover, since the surface of the optical recording medium 110 is not brought into tight contact with the tray, ejection of the optical recording medium 110 becomes easier.
However, such a metal mold as is employed in the injection molding described above is expensive, leading to an increase in the production cost of the substrate 111.
Further, forming ridgy resin films in various forms requires the use of metal molds corresponding to their respective shapes.
For forming the ridgy resin film without using a metal mold, there may be proposed a method including applying a resin liquid containing a photoreactive resin onto the surface of the substrate and curing the resin liquid through the irradiation of ultraviolet rays.
However, according to this method, if the viscosity of the resin liquid is high, the resulting ridgy resin film will be wide. Particularly, in the case where the resin liquid is applied in the form of a ring, as described above, since the starting position of resin supply and its end position overlap and the resin liquid is supplied there excessively, the resulting film will be wide only at the point of overlap.
On the other hand, if the viscosity of the resin liquid is low, the resin liquid cannot rise from the surface of the substrate and therefore the surface of the resulting ridgy resin film will be lowered.
In any case, in the technique of applying the resin liquid, it is difficult to form a ridgy resin film which rises for a sufficient height and has an even width.
The present invention was made to solve the above-described problems faced in the prior art. An object of the present invention is to provide a process for forming a ridgy resin film uniform in width without using a mold, particularly a ring-shape ridgy resin film which is uniform in width.
For solving the above-mentioned problems, the present invention is a process for forming a ridgy resin film, comprising the steps of: forming a first concave and a second concave on a surface of a plate substrate to make an area between the first and second concaves as a resin film formation area; supplying a resin liquid containing a photopolymerizable resin onto a surface of the resin film formation area to form a resin liquid layer consisting the resin liquid; and curing the resin liquid layer to form a ridgy resin film.
The present invention is the process for forming a ridgy resin film, wherein the resin liquid layer is cured by irradiation with ultraviolet rays.
The present invention is the process for forming a ridgy resin film, wherein during the step of forming the first concave and the second concave, a boundary between the resin film formation area and the first concave and that between the resin film formation area and the second concave are raised to form ridges, and the ridgy resin film is formed between the ridges.
The present invention is the process for forming a ridgy resin film, wherein the first and second concaves are formed by scraping the surface of the substrate by pressing an excavator against the surface of the substrate.
The present invention is the process for forming a ridgy resin film, the first and second concaves are formed by irradiating the surface of the substrate with a laser beam.
The present invention is the process for forming a ridgy resin film, wherein the first and second concaves are formed in concentric relation.
The present invention is the process for forming a ridgy resin film, wherein the viscosity of the resin liquid at 25xc2x0 C. is not lower than 10 mPaxc2x7s nor higher than 1,000 mPaxc2x7s.
The present invention is the process for forming a ridgy resin film, wherein the viscosity of the resin liquid at 25xc2x0 C. exceeds 100 mPaxc2x7s.
The present invention is the process for forming a ridgy resin film, wherein the glass transition temperature of the resin forming the ridgy resin film is not lower than 60xc2x0 C. and below 100xc2x0 C.
The present invention is the process for forming a ridgy resin film, wherein the height from the surface of the resin film formation area to the surface of the ridgy resin film is 3 xcexcm or higher.
The present invention is a process for producing a recording medium molded in the form of a disk and having a recording layer and a resin layer provided on the recording layer, the process comprising the steps of; forming ring-shaped first and second concaves on a surface of the resin layer with the center of the recording medium as the centers to form an area between the first and second concaves as a resin film formation area; supplying a resin liquid containing a photopolymerizable resin onto the resin film formation; and curing the resin liquid layer to give a ridgy resin film.
The present invention is an optical recording medium molded in the form of a disk and having a recording layer and a resin layer provided on the recording layer, wherein ring-shaped first and second concaves with the center of said recording medium as the centers, a resin film formation area between said first and second concaves, and a ridgy resin film formed in said resin film formation area are formed on a surface of said resin layer, and said ridgy resin film is raised above a surface of said resin layer.
The present invention is the recording medium, wherein the resin layer is made of a polycarbonate resin.
Since the present invention has the structure as described above and the first and second concaves formed on the surface of the substrate are spaced a given distance apart from each other, a ridgy resin film having a predetermined width can be obtained by supplying a resin liquid onto the land between the first and second concaves and then curing the resin liquid supplied.
In the case where the first and second concaves are formed using an excavator or a laser beam, the edges of the openings of the first and second concaves are raised to constitute ridges. Of these ridges, between two ridges adjacent to each other lies a land being part of the substrate, and it is level with the rest of the plane substrate. Even when the resin liquid is supplied onto the land between these two ridges, dripping or overflow of the resin liquid does not take place, for the ridges dam up the flow. Moreover, due to its surface tension, the surface of the resin liquid supplied rises high from the surface of the substrate. By curing the resin liquid in this state, there is provided a ridgy resin film free from dripping or overflow.
A ridgy resin film in the form of, as a whole, a ring is formed by making the first and second concaves in concentraic relation and supplying the resin liquid onto the land therebetween.
Although, at the point of overlap (the juncture of the ring), the resin liquid is supplied in an amount larger than that at any other point, the ridges similarly prevents the resin liquid from overflowing, so that the width of the ring at the juncture will be the same as that at any other point.
According to the process for forming a ridgy resin film of the present invention, it is possible to form a ridgy resin film of a desired form on a surface of an arbitrarily selected substrate.